Formation of formic acid from renewable biomass resources is of great interest since formic acid is a widely used platform chemical and has recently been regarded as an important liquid hydrogen carrier. Herein, a novel approach is reported for the conversion of glucose, the constituent carbohydrate from cellulose fraction of biomass, to formic acid under mild hydrothermal conditions with simultaneous reduction of Ag2O to Ag. Results showed that glucose was selectively converted to formic acid with an optimum yield of 40.7% at a mild reaction temperature of 135 for 30 min. In addition, Ag2O was used as a solid oxidant for the glucose oxidation, which avoids the use of traditionally dangerous liquid oxidant H2O2. Furthermore, complete conversion of Ag2O to Ag can be achieved. This study not only developed a new method for value-added chemical production from renewable biomass but also explored an alternative low-carbon and energy-saving route for silver extraction and recovery.